Install HAProxy 2.x in CentOS amphora images

The CentOS NFV SIG [1] maintains a RPM repository with extra and newer
packages. This includes HAProxy 2.2 as of this time of writing.

[1] https://wiki.centos.org/SpecialInterestGroup/NFV

Change-Id: I2f64a44c566f138c58ea4be53b1ff90a52012950

elements/haproxy-octavia/pre-install.d/01-repositories

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+set -eu
+set -o xtrace
+
+if [ "$DISTRO_NAME" == "centos" ]; then
+    dnf install -y dnf-plugins-core centos-release-nfv-common
+    # REVISIT(cgoncalves): replace arch if-else + GPG with release RPM once available
+    if [[ "$ARCH" =~ (aarch64|arm64) ]]; then
+        yum_arch=aarch64
+    elif [[ "$ARCH" =~ (ppc64le|ppc64el) ]]; then
+        yum_arch=ppc64le
+    elif [[ "$ARCH" =~ (x86_64|amd64) ]]; then
+        yum_arch=x86_64
+    else
+        echo "ERROR: Unsupported architecture $ARCH"
+        exit 1
+    fi
+    dnf config-manager --add-repo http://mirror.centos.org/centos/8/nfv/${yum_arch}/network-extras
+    echo gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-SIG-NFV >> /etc/yum.repos.d/mirror.centos.org_centos_8_nfv_*_network-extras.repo
+fi

releasenotes/notes/add-haproxy2-centos-063beb304409d141.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    CentOS-based amphora images will now install HAProxy version 2.2 maintained
+    by CentOS NFV SIG. Other supported distributions (Ubuntu Bionic, RHEL 8)
+    remain untouched.